The invention is directed to a valve arrangement for controlling the flow of mediums, specifically gases or liquids, in pipelines or similar conduits.
Proportional valves have been previously known where the flow through the valve is controllable by proportional adjustment of a slide and/or the valve head. However, such valves are expensive in design, and normally are too unreactive or slow-acting for application in quick control processes. Lastly, these valves possess a limited control range so that in the case of a valve designed for a high flow rate, the valve can normally not be adjusted to provide a small amount of flow.
It has already been suggested to employ for flow control simple on-off valves which are periodically opened for a brief period of time and where the duration of the open time determines the amount of flow. However, with such valves, it is not possible to adjust to very small flow rates since the preselected open time must not fall below a specific value in order to ensure that the valve head will actually lift off the valve seat. While it is possible to arrange several of such on-off valves having various flow rates in a parallel fashion and activate them so that the valve which provides the desired flow will be activated, such an arrangement is very expensive due to the use of a plurality of such valves.